Binder composition for non-aqueous secondary battery electrode, slurry composition for non-aqueous secondary battery electrode, electrode for non-aqueous secondary battery, and non-aqueous secondary battery

ABSTRACT

A binder composition for a non-aqueous secondary battery electrode contains a particulate polymer A and a particulate polymer B. The particulate polymer A is a block copolymer including an aromatic vinyl monomer unit and an aliphatic conjugated diene monomer unit having a carbon number of 4 or more. The particulate polymer B is a random copolymer including a (meth)acrylic acid ester monomer unit in a proportion of not less than 20.0 mass % and not more than 80.0 mass %.

TECHNICAL FIELD

The present disclosure relates to a binder composition for a non-aqueoussecondary battery electrode, a slurry composition for a non-aqueoussecondary battery electrode, an electrode for a non-aqueous secondarybattery, and a non-aqueous secondary battery.

BACKGROUND

Non-aqueous secondary batteries (hereinafter, also referred to simply as“secondary batteries”) such as lithium ion secondary batteries havecharacteristics such as compact size, light weight, high energy-density,and the ability to be repeatedly charged and discharged, and are used ina wide variety of applications. Consequently, in recent years, studieshave been made to improve electrodes and other battery components withthe aim of achieving even higher non-aqueous secondary batteryperformance.

An electrode for a secondary battery, such as a lithium ion secondarybattery, generally includes a current collector and an electrode mixedmaterial layer formed on the current collector. The electrode mixedmaterial layer is formed, for example, by applying, onto the currentcollector, a slurry composition in which an electrode active material, abinder-containing binder composition, and so forth are dispersed in adispersion medium (solvent), and drying the applied slurry composition.

In recent years, attempts have been made to improve binder compositionsused in formation of electrodes in order to achieve further improvementof secondary battery performance (for example, refer to Patent

Literature (PTL) 1 and 2).

PTL 1 discloses a lithium ion secondary battery including a negativeelectrode formed using a slurry composition for an electrode thatcontains only styrene-ethylene-butylene-styrene block copolymerizationpolymer particles as a binder component.

PTL 2 discloses a binder composition for a non-aqueous secondary batteryelectrode in which a particulate polymer A and a particulate polymer Bhaving different particle diameters to one another are compounded in aspecific ratio. More specifically, the particulate polymer A can includean aliphatic conjugated diene monomer unit in a proportion of not lessthan 50 mass % and not more than 90 mass % and can include an aromaticvinyl monomer unit in a proportion of not less than 10 mass % and notmore than 50 mass %. Moreover, the particulate polymer B can include analiphatic conjugated diene monomer unit in a proportion of not less than30 mass % and not more than 60 mass %.

CITATION LIST Patent Literature

PTL 1: WO 2016/080144 A1

PTL 2: WO 2017/056404 A1

SUMMARY Technical Problem

However, there has been demand for further improvement of secondarybattery performance in recent years, and the conventional slurrycomposition and binder composition described above leave room forimprovement in terms of further improving battery characteristics suchas low-temperature output characteristics and cycle characteristics ofan obtained non-aqueous secondary battery.

Accordingly, one objective of the present disclosure is to provide abinder composition for a non-aqueous secondary battery electrode and aslurry composition for a non-aqueous secondary battery electrode withwhich it is possible to form an electrode for a non-aqueous secondarybattery that can cause a non-aqueous secondary battery to displayexcellent low-temperature output characteristics and cyclecharacteristics.

Another objective of the present disclosure is to provide an electrodefor a non-aqueous secondary battery that can cause a non-aqueoussecondary battery to display excellent low-temperature outputcharacteristics and cycle characteristics.

Yet another objective of the present disclosure is to provide anon-aqueous secondary battery having excellent battery characteristicssuch as low-temperature output characteristics and cyclecharacteristics.

Solution to Problem

The inventors conducted diligent investigation with the aim of solvingthe problem set forth above. The inventors discovered that by using abinder composition that contains both a particulate polymer that is ablock copolymer including an aromatic vinyl monomer unit and analiphatic conjugated diene monomer unit having a carbon number of 4 ormore and a particulate polymer that is a random copolymer including a(meth)acrylic acid ester monomer unit in a proportion of not less than20 mass % and not more than 80 mass %, it is possible to form anelectrode for a non-aqueous secondary battery that can cause anon-aqueous secondary battery to display excellent low-temperatureoutput characteristics and cycle characteristics, and, in this manner,the inventors completed the present disclosure.

Specifically, the present disclosure aims to advantageously solve theproblem set forth above by disclosing a binder composition for anon-aqueous secondary battery electrode comprising a particulate polymerA and a particulate polymer B, wherein the particulate polymer A is ablock copolymer including an aromatic vinyl monomer unit and analiphatic conjugated diene monomer unit having a carbon number of 4 ormore, and the particulate polymer B is a random copolymer including a(meth)acrylic acid ester monomer unit in a proportion of not less than20.0 mass % and not more than 80.0 mass %. When an electrode is formedusing a binder composition containing a particulate polymer A that is ablock copolymer including an aromatic vinyl monomer unit and analiphatic conjugated diene monomer unit and a particulate polymer B thatis a random copolymer including a (meth)acrylic acid ester monomer unitin the specific proportion set forth above in this manner, a non-aqueoussecondary battery that includes the electrode can be caused to displayexcellent low-temperature output characteristics and cyclecharacteristics.

Note that a “monomer unit” of a polymer referred to in the presentdisclosure is a “repeating unit derived from the monomer that isincluded in a polymer obtained using the monomer”. The proportion inwhich a monomer unit is included in a polymer can be measured by ¹H-NMR.Also note that in the present disclosure, “(meth)acryl” is used toindicate “acryl” or “methacryl”.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the particulate polymer A preferablyincludes a graft portion. When the particulate polymer A includes agraft portion, aggregation of compounded components such as an electrodeactive material can be inhibited during application of a slurrycomposition for a non-aqueous secondary battery electrode that isproduced using the binder composition.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the graft portion of the particulatepolymer A preferably includes an acidic group-containing monomer unit ina proportion of not less than 0.1 mass % and not more than 30.0 mass %when the particulate polymer A is taken to be 100 mass % overall. Whenthe particulate polymer A includes a graft portion including an acidicgroup-containing monomer unit and when the proportion in which theacidic group-containing monomer unit is included in the graft portionrelative to the overall particulate polymer A is within the range setforth above, it is possible to increase stability and improve coatingdensity of a slurry composition for a non-aqueous secondary batteryelectrode produced using the binder composition, and also to betterinhibit aggregation of compounded components such as an electrode activematerial during application of the slurry composition.

Note that the proportion constituted in the overall particulate polymerA by the acidic group-containing monomer unit that is a constituent ofthe graft portion can be measured by a method described in the EXAMPLESsection of the present specification.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the particulate polymer A preferablyincludes the aromatic vinyl monomer unit in a proportion of not lessthan 10.0 mass % and not more than 30.0 mass %. When the particulatepolymer A includes the aromatic vinyl monomer unit in the specificproportion set forth above, it is possible to increase stability of aslurry composition for a non-aqueous secondary battery electrodeproduced using the binder composition, and also to further improvelow-temperature output characteristics and cycle characteristics of asecondary battery including an electrode formed using the slurrycomposition for a non-aqueous secondary battery electrode.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, content of the particulate polymer A ispreferably not less than 20.0 mass % and not more than 80.0 mass % whentotal content of the particulate polymer A and the particulate polymer Bis taken to be 100 mass %. When the proportion constituted by theparticulate polymer A among the total amount of the particulate polymersA and B is within the range set forth above, low-temperature outputcharacteristics and cycle characteristics of an obtained secondarybattery can be further improved.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the particulate polymer B preferablyincludes a monomer unit selected from an aromatic vinyl monomer unit anda vinyl cyanide monomer unit in a proportion of not less than 10 mass %and not more than 70 mass %. When the particulate polymer B includes amonomer unit selected from an aromatic vinyl monomer unit and a vinylcyanide monomer unit in a proportion within the range set forth above,cycle characteristics of an obtained secondary battery can be furtherimproved.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the particulate polymer B preferablyfurther includes an acidic group-containing monomer unit in a proportionof not less than 1.0 mass % and not more than 15.0 mass %. When theparticulate polymer B includes an acidic group-containing monomer unitin a proportion within the range set forth above, low-temperature outputcharacteristics and cycle characteristics of an obtained secondarybattery can be further improved.

The present disclosure also aims to advantageously solve the problem setforth above by disclosing a slurry composition for a non-aqueoussecondary battery electrode comprising any one of the bindercompositions for a non-aqueous secondary battery electrode set forthabove. When an electrode is formed using a slurry composition thatcontains any one of the binder compositions set forth above in thismanner, low-temperature output characteristics and cycle characteristicsof a secondary battery including the electrode can be further improved.

The present disclosure also aims to advantageously solve the problem setforth above by disclosing an electrode for a non-aqueous secondarybattery comprising an electrode mixed material layer formed using anyone of the slurry compositions set forth above, wherein the electrodemixed material layer has a density of 1.70 g/cm³ or more. Through use ofany one of the slurry compositions set forth above, it is possible toform a high-density electrode that can enhance low-temperature outputcharacteristics and cycle characteristics of a secondary battery. Notethat the density of the electrode mixed material layer can be calculatedusing the mass of the electrode mixed material layer per unit area andthe thickness of the electrode mixed material layer.

The present disclosure also aims to advantageously solve the problem setforth above by disclosing a non-aqueous secondary battery comprising theelectrode for a non-aqueous secondary battery set forth above. Asecondary battery that includes the electrode for a non-aqueoussecondary battery set forth above has excellent low-temperature outputcharacteristics and cycle characteristics.

Advantageous Effect

According to the present disclosure, it is possible to provide a bindercomposition for a non-aqueous secondary battery electrode and a slurrycomposition for a non-aqueous secondary battery electrode with which itis possible to form an electrode for a non-aqueous secondary batterythat can cause a non-aqueous secondary battery to display excellentlow-temperature output characteristics and cycle characteristics.

Moreover, according to the present disclosure, it is possible to providean electrode for a non-aqueous secondary battery that can cause anon-aqueous secondary battery to display excellent low-temperatureoutput characteristics and cycle characteristics.

Furthermore, according to the present disclosure, it is possible toprovide a non-aqueous secondary battery having excellent batterycharacteristics such as low-temperature output characteristics and cyclecharacteristics.

DETAILED DESCRIPTION

The following provides a detailed description of embodiments of thepresent disclosure.

The presently disclosed binder composition for a non-aqueous secondarybattery electrode is a composition for use in the production of anon-aqueous secondary battery and can be used to produce the presentlydisclosed slurry composition for a non-aqueous secondary batteryelectrode, for example. Moreover, the presently disclosed slurrycomposition for a non-aqueous secondary battery electrode can be used information of an electrode of a non-aqueous secondary battery and issuitable, in particular, for use in formation of a negative electrode ofa non-aqueous secondary battery.

Furthermore, the presently disclosed electrode for a non-aqueoussecondary battery is formed from the presently disclosed slurrycomposition for a non-aqueous secondary battery electrode. Also, thepresently disclosed non-aqueous secondary battery includes the presentlydisclosed electrode for a non-aqueous secondary battery.

(Binder Composition for Non-Aqueous Secondary Battery Electrode)

The presently disclosed binder composition contains a particulatepolymer A and a particulate polymer B, and may optionally furthercontain other components that can be compounded in an electrode of asecondary battery. Moreover, the presently disclosed binder compositionfor a non-aqueous secondary battery electrode can further contain asolvent such as water. Features of the presently disclosed bindercomposition are that the particulate polymer A is a block copolymerincluding an aromatic vinyl monomer unit and an aliphatic conjugateddiene monomer unit having a carbon number of 4 or more, and theparticulate polymer B is a random copolymer including a (meth)acrylicacid ester monomer unit in a proportion of not less than 20 mass % andnot more than 80 mass %.

The particulate polymer A is a block copolymer including an aromaticvinyl monomer unit and is a polymer that can favorably follow expansionand contraction of an electrode active material accompanying repeatedcharging and discharging. The particulate polymer B is a randomcopolymer including a (meth)acrylic acid ester monomer unit in aspecific proportion and is a polymer that itself has high flexibilityand that can also increase slurry composition stability. Consequently, acoating film formed on a substrate through application of a slurrycomposition that is produced using the binder composition containingboth of these particulate polymers A and B has high dispersibility ofsolid content such as an electrode active material. Moreover, when thiscoating film is pressed to form a high-density electrode mixed materiallayer, it is presumed that good formation of a high-density electrodemixed material layer is possible without application of excessivepressure because an appropriate degree of flexibility can be displayedby the particulate polymer B. Consequently, a slurry compositionproduced using the binder composition containing both the particulatepolymer A and the particulate polymer B can form an electrode that haslow internal resistance and excellent resistance to deformation inaccompaniment to repeated charging and discharging. Therefore, thepresently disclosed binder composition enables formation of an electrodefor a non-aqueous secondary battery that can cause a non-aqueoussecondary battery to display excellent low-temperature outputcharacteristics and cycle characteristics.

<Particulate Polymer A>

In an electrode produced by forming an electrode mixed material layer ona current collector using a slurry composition for a non-aqueoussecondary battery electrode that is produced using the bindercomposition, the particulate polymer A holds components contained in theelectrode mixed material layer to prevent these components detachingfrom the electrode mixed material layer (i.e., the particulate polymer Afunctions as a binder). Note that the particulate polymer A is in theform of water-insoluble particles formed by a specific block copolymer.The particulate polymer A includes at least the specific block copolymerand may include components other than the specific block copolymer suchas components that are unavoidably mixed in at the production stage.

When particles are referred to as “water-insoluble” in the presentdisclosure, this means that when 0.5 g of the particles are dissolved in100 g of water at a temperature of 25° C., insoluble content is 90 mass% or more.

<<Structure and Chemical Composition>>

The particulate polymer A is a block copolymer including an aromaticvinyl monomer unit and an aliphatic conjugated diene monomer unit havinga carbon number of 4 or more. More specifically, the particulate polymerA is a block copolymer including a block region formed by an aromaticvinyl monomer unit (hereinafter, also referred to simply as an “aromaticvinyl block region”) and a block region formed by an aliphaticconjugated diene monomer unit having a carbon number of 4 or more(hereinafter, also referred to simply as a “conjugated diene blockregion”). The aromatic vinyl block region is formed by only an aromaticvinyl monomer unit. The conjugated diene block region is preferablyformed by only a conjugated diene monomer unit but may, besides theconjugated diene monomer unit, include an alkylene structural unit.Moreover, the conjugated diene block region may include an extremelysmall amount of a constitutional unit other than the conjugated dienemonomer unit and the alkylene structural unit. The proportion of suchother constitutional units is preferably 30 mass % or less when theamount of all repeating units in the block copolymer is taken to be 100mass %.

The aromatic vinyl block region and the conjugated diene block regionare present adjacently to one another in the block copolymer. Thecopolymer can include one aromatic vinyl block region or a plurality ofaromatic vinyl block regions. Likewise, the copolymer can include oneconjugated diene block region or a plurality of conjugated diene blockregions. The copolymer may also include other regions.

The particulate polymer A including the aromatic vinyl block region andthe conjugated diene block region has both rigidity and flexibility, andcan favorably follow expansion and contraction of an electrode activematerial accompanying repeated charging and discharging of a secondarybattery.

[Aromatic Vinyl Block Region]

The aromatic vinyl block region is a region that essentially includesonly an aromatic vinyl monomer unit as a repeating unit as previouslydescribed.

Note that a single aromatic vinyl block region may be composed of just asingle type of aromatic vinyl monomer unit or may be composed of aplurality of types of aromatic vinyl monomer units, but is preferablycomposed of just a single type of aromatic vinyl monomer unit.

Moreover, a single aromatic vinyl block region may include a couplingmoiety (i.e., aromatic vinyl monomer units of a single aromatic vinylblock region may be linked with a coupling moiety interposedin-between).

In a case in which the block copolymer includes a plurality of aromaticvinyl block regions, the types and proportions of aromatic vinyl monomerunits in the plurality of aromatic vinyl block regions may be the sameor different, but are preferably the same.

Examples of aromatic vinyl monomers that can form an aromatic vinylmonomer unit of the aromatic vinyl block region in the block copolymerinclude styrene, styrene sulfonic acid and salts thereof,a-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene,chlorostyrene, and vinylnaphthalene. Of these aromatic vinyl monomers,styrene is preferable. Although one of these aromatic vinyl monomers maybe used individually or two or more of these aromatic vinyl monomers maybe used in combination, it is preferable that one of these aromaticvinyl monomers is used individually. In particular, styrene ispreferable.

The proportion constituted by the aromatic vinyl monomer unit in theblock copolymer when the amount of all repeating units in the blockcopolymer (monomer units and structural units; inclusive of graftportion repeating units in a case in which the block copolymer includesa graft portion) is taken to be 100 mass % is preferably 10.0 mass % ormore, more preferably 12.0 mass % or more, and even more preferably 15.0mass % or more, and is preferably 30.0 mass % or less, more preferably28.0 mass % or less, and even more preferably 26.0 mass % or less. Notethat the proportion constituted by the aromatic vinyl monomer unit inthe block copolymer is normally the same as the proportion constitutedby the aromatic vinyl block region in the block copolymer.

When the proportion constituted by the aromatic vinyl monomer unit inthe block copolymer is not less than any of the lower limits set forthabove, it is possible to increase close adherence between an electrodeactive material and the particulate polymer A when an electrode isformed and to effectively inhibit swelling of the electrode accompanyingrepeated charging and discharging. Moreover, when the proportionconstituted by the aromatic vinyl monomer unit is not less than any ofthe lower limits set forth above, slurry stability of a slurrycomposition containing the binder composition can be increased, andbattery characteristics such as low-temperature output characteristicsand cycle characteristics of an obtained secondary battery can beenhanced. Furthermore, when the proportion constituted by the aromaticvinyl monomer unit in the block copolymer is not more than any of theupper limits set forth above, it is possible to form an electrode havinghigh affinity with electrolyte solution. Note that the affinity of anelectrode with electrolyte solution tends to be lower in a case in whichthe electrode is densified.

However, an electrode formed using the presently disclosed bindercomposition has high affinity with electrolyte solution even in asituation in which the electrode is densified. Consequently, anelectrode formed using the presently disclosed binder composition hashigh electrolyte solution injectability.

[Aliphatic Conjugated Diene Block Region]

The aliphatic conjugated diene block region is a region essentiallyincluding an aliphatic conjugated diene monomer unit having a carbonnumber of 4 or more (hereinafter, also referred to simply as an“aliphatic conjugated diene monomer unit”) as a repeating unit aspreviously described.

A single aliphatic conjugated diene block region can be composed of asingle type of aliphatic conjugated diene monomer unit or a plurality oftypes of aliphatic conjugated diene monomer units.

Moreover, a single aliphatic conjugated diene block region may include acoupling moiety (i.e., aliphatic conjugated diene monomer units of asingle aliphatic conjugated diene block region may be linked with acoupling moiety interposed in-between).

In a case in which the block copolymer includes a plurality of aliphaticconjugated diene block regions, the types and proportions of aliphaticconjugated diene monomer units in the plurality of aliphatic conjugateddiene block regions may be the same or different.

Examples of the aliphatic conjugated diene monomer unit of the aliphaticconjugated diene block region of the block copolymer include conjugateddiene compounds having a carbon number of 4 or more such as1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene.One of these conjugated diene compounds may be used individually, or twoor more of these conjugated diene compounds may be used in combination.Of these conjugated diene compounds, 1,3-butadiene and isoprene arepreferable, and isoprene is particularly preferable from a viewpoint offurther improving process adhesiveness of a battery component.

The proportion constituted by the aliphatic conjugated diene monomerunit in the block copolymer when the amount of all repeating units inthe block copolymer is taken to be 100 mass % is preferably 50.0 mass %or more, more preferably 55.0 mass % or more, and even more preferably60.0 mass % or more, and is preferably 90.0 mass % or less, morepreferably 87.5 mass % or less, and even more preferably 85.0 mass % orless. When the proportion constituted by the aliphatic conjugated dienemonomer unit in the block copolymer is not less than any of the lowerlimits set forth above, the block copolymer can be provided with asuitable degree of flexibility. This can improve ability to followexpansion and contraction of an electrode active material accompanyingrepeated charging and discharging by increasing the flexibility of anobtained electrode, and, as a result, can effectively inhibit swellingof the electrode. Moreover, when the proportion constituted by thealiphatic conjugated diene monomer unit in the block copolymer is notmore than any of the upper limits set forth above, it is possible toprevent the block copolymer from becoming too flexible and to enhancecycle characteristics of an obtained secondary battery.

The aliphatic conjugated diene monomer unit may include an alkylenestructural unit. The alkylene structural unit is a repeating unitcomposed only of an alkylene structure represented by a general formula—C_(n)H_(2n)— (n is an integer of 2 or more).

Although the alkylene structural unit may be linear or branched, thealkylene structural unit is preferably linear (i.e., is preferably alinear alkylene structural unit). Moreover, the alkylene structural unitpreferably has a carbon number of 4 or more (i.e., n in the precedinggeneral formula is preferably an integer of 4 or more).

No specific limitations are placed on the method by which the alkylenestructural unit is introduced into the aliphatic conjugated diene blockregion. For example, a method in which a polymer including an aliphaticconjugated diene block region is hydrogenated so that an aliphaticconjugated diene monomer unit included in the aliphatic conjugated dieneblock region is converted to an alkylene structural unit may be adopted.

—Graft Portion—

The aliphatic conjugated diene block region of the particulate polymer Apreferably includes a graft portion. In other words, the particulatepolymer A preferably has a structure in which a polymer that becomes agraft portion is bonded to an aliphatic conjugated diene block region ofa chain portion including an aromatic vinyl block region and analiphatic conjugated diene block region, which corresponds to a “trunkportion”. The inclusion of a graft portion in the particulate polymer Acan inhibit aggregation of compounded components such as an electrodeactive material during application of a slurry composition for anon-aqueous secondary battery electrode that is produced using thebinder composition. This is presumed to be due to the graft portionphysically inhibiting surface contact amongst the particulate polymer Aand between the particulate polymer A and other components.

Examples of repeating units that can be included in the graft portion ofthe particulate polymer A include an acidic group-containing monomerunit, a (meth)acrylic acid ester monomer unit, and an aromatic vinylmonomer unit.

Examples of acidic group-containing monomers include monomers that havean acidic group such as carboxy group-containing monomers, sulfogroup-containing monomers, and phosphate group-containing monomers.

Examples of carboxy group-containing monomers include monocarboxylicacids, derivatives of monocarboxylic acids, dicarboxylic acids, acidanhydrides of dicarboxylic acids, and derivatives of dicarboxylic acidsand acid anhydrides thereof.

Examples of monocarboxylic acids include acrylic acid, methacrylic acid,and crotonic acid.

Examples of derivatives of monocarboxylic acids include 2-ethylacrylicacid, isocrotonic acid, a-acetoxyacrylic acid, β-trans-aryloxyacrylicacid, and α-chloro-β-E-methoxyacrylic acid.

Examples of dicarboxylic acids include maleic acid, fumaric acid, anditaconic acid.

Examples of derivatives of dicarboxylic acids include methylmaleic acid,dimethylmaleic acid, phenylmaleic acid, chloromaleic acid,dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters suchas nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, andfluoroalkyl maleates.

Examples of acid anhydrides of dicarboxylic acids include maleicanhydride, acrylic anhydride, methylmaleic anhydride, and dimethylmaleicanhydride.

Furthermore, an acid anhydride that produces a carboxy group uponhydrolysis can also be used as a carboxy group-containing monomer.

Examples of sulfo group-containing monomers include vinyl sulfonic acid,methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylicacid 2-sulfoethyl, 2-acrylamido-2-methylpropane sulfonic acid, and3-allyloxy-2-hydroxypropane sulfonic acid.

Examples of phosphate group-containing monomers include2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethylphosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

Note that in the present disclosure, “(meth)allyl” is used to indicate“allyl” and/or “methallyl”, and “(meth)acryloyl” is used to indicate“acryloyl” and/or “methacryloyl”.

Examples of (meth)acrylic acid ester monomers include acrylic acid alkylesters such as methyl acrylate, ethyl acrylate, n-propyl acrylate,isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutylacrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptylacrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decylacrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate;and methacrylic acid alkyl esters such as methyl methacrylate, ethylmethacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butylmethacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentylmethacrylate, isopentyl methacrylate, hexyl methacrylate, heptylmethacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonylmethacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecylmethacrylate, and stearyl methacrylate.

Examples of aromatic vinyl monomers include the same aromatic vinylmonomers as can be used in formation of the aromatic vinyl block region.

The various monomers described above that can be used to form repeatingunits included in the graft portion of the block copolymer may be onetype used individually or two or more types used in combination. Acarboxy group-containing monomer is preferable as an acidicgroup-containing monomer for forming an acidic group-containing monomerunit included in the graft portion of the block copolymer. Of carboxygroup-containing monomers, methacrylic acid, itaconic acid, and acrylicacid are more preferable, and methacrylic acid is particularlypreferable.

No specific limitations are placed on the method by which the graftportion is introduced into the block copolymer. For example, a blockcopolymer having a structure in which a polymer of a graft portion isbonded to an aliphatic conjugated diene monomer unit of a polymer of atrunk portion can be obtained by producing the specific block copolymerset forth above and then performing graft polymerization of an acidicgroup-containing monomer such as set forth above, or the like, by aknown method, with the produced block copolymer as a trunk portion.

In a case in which the block copolymer includes a graft portion, theproportion constituted by an acidic group-containing monomer unitincluded in the graft portion in the block copolymer when the amount ofall repeating units in the block copolymer is taken to be 100 mass % ispreferably 0.1 mass % or more, more preferably 0.2 mass % or more, andeven more preferably 0.5 mass % or more, and is preferably 30.0 mass %or less, more preferably 15.0 mass % or less, and even more preferably5.0 mass % or less.

When the proportion constituted by the acidic group-containing monomerunit is not less than any of the lower limits set forth above, slurrystability of a slurry composition containing the binder composition canbe increased, and thus coating density when the slurry composition isapplied onto a substrate to form an electrode can be increased.Moreover, aggregation of compounded components such as an electrodeactive material in an obtained electrode can be well inhibited, and, asa result, low-temperature output characteristics and cyclecharacteristics of a secondary battery including the obtained electrodecan be improved. Also, when the proportion constituted by the acidicgroup-containing monomer unit is not less than any of the lower limitsset forth above, affinity with electrolyte solution of an electrode thatcan be formed using a slurry composition containing the bindercomposition can be improved, which enables formation of a secondarybattery having good electrolyte solution injectability. Furthermore,when the proportion constituted by the acidic group-containing monomerunit is not more than any of the upper limits set forth above, anelectrode that can be formed using a slurry composition containing thebinder composition can be provided with higher adhesiveness to anotherbattery component such as a separator, and, as a result, swelling of theelectrode accompanying repeated charging and discharging can beeffectively inhibited.

[Diblock Content]

The block copolymer contained in the polymer particles can be composedby one or a plurality of polymer chains. The polymer chains composingthe block copolymer may be any structures such as a diblock structureincluding one each of an aromatic block region and an aliphaticconjugated diene block region and a triblock structure including threeregions (for example, a structure including an aromatic vinyl blockregion, an aliphatic conjugated diene block region, and an aromaticvinyl block region that are linked in this order).

The proportion constituted by diblock structures in the particulatepolymer A (i.e., the diblock content) when the mass of the overall blockcopolymer is taken to be 100 mass % is preferably 1 mass % or more,preferably 3 mass % or more, and more preferably 5 mass % or more, andis preferably 60 mass % or less, preferably 50 mass % or less, and morepreferably 40 mass % or less. When the diblock content in theparticulate polymer A is not less than any of the lower limits set forthabove, an excessive increase in internal stress of an obtained electrodecan be inhibited, and swelling of the electrode accompanying chargingand discharging can be effectively inhibited. Moreover, when the diblockcontent in the particulate polymer A is not more than any of the upperlimits set forth above, an electrode that can be formed using a slurrycomposition containing the binder composition can be provided withhigher adhesiveness to another battery component such as a separator,and, as a result, swelling of the electrode accompanying repeatedcharging and discharging can be effectively inhibited.

The diblock content can be reduced by carrying out a subsequentlydescribed coupling reaction in production of the block copolymer, forexample. Moreover, the diblock content can be adjusted by altering thetype and amount of a coupling agent used in production of the blockcopolymer. Note that the diblock content can be measured by a methoddescribed in the EXAMPLES section of the present specification.

[Volume-Average Particle Diameter]

The volume-average particle diameter of the particulate polymer A ispreferably 0.10 μm or more, more preferably 0.12 μm or more, and evenmore preferably 0.15 μm or more, and is preferably 5.00 μm or less, morepreferably 2.00 μm or less, and even more preferably 1.50 μm or less.When the volume-average particle diameter of the particulate polymer Ais not less than any of the lower limits set forth above, closeadherence between an electrode and another battery component such as aseparator can be increased, and electrode swelling accompanying chargingand discharging can be effectively inhibited. Moreover, when thevolume-average particle diameter of the particulate polymer A is notmore than any of the upper limits set forth above, an excessive decreasein specific surface area of the particulate polymer A can be inhibited,adhesive ability that can be displayed by the particulate polymer A canbe sufficiently increased, and, as a result, cycle characteristics of anobtained secondary battery can be improved.

Note that the volume-average particle diameter of the particulatepolymer A can be measured by a method described in the EXAMPLES sectionof the present specification.

<<Production Method of Particulate Polymer A>>

The particulate polymer A is preferably produced by, for example, blockpolymerizing the monomers set forth above in an organic solvent toobtain a solution of a block copolymer, and then adding water to theobtained solution of the block copolymer and performing emulsification(i.e., phase-inversion emulsification) to form particles of the blockpolymer and obtain a water dispersion of polymer particles. In addition,graft polymerization is preferably performed with respect to the blockcopolymer. The block polymer can also be hydrogenated as necessary.

No specific limitations are placed on the method of block polymerizationin production of the block copolymer. For example, production may becarried out by polymerizing a first monomer component, adding a secondmonomer component, differing from the first monomer component, to theresultant solution and performing polymerization thereof, and furtherrepeating addition and polymerization of monomer components asnecessary.

The organic solvent used as the reaction solvent is not specificallylimited and can be selected as appropriate depending on the types ofmonomers and so forth.

The block copolymer obtained through block polymerization as describedabove is preferably subjected to a coupling reaction using a couplingagent. The coupling reaction can, for example, cause the terminals ofdiblock structures contained in the block copolymer to bond to oneanother through the coupling agent to thereby convert the diblockstructures to a triblock structure (i.e., the diblock content can bereduced).

Examples of coupling agents that can be used in the coupling reactioninclude, without any specific limitations, difunctional coupling agents,trifunctional coupling agents, tetrafunctional coupling agents, andcoupling agents having a functionality of 5 or higher.

Examples of difunctional coupling agents include difunctionalhalosilanes such as dichlorosilane, monomethyldichlorosilane, anddichlorodimethylsilane; difunctional haloalkanes such as dichloroethane,dibromoethane, methylene chloride, and dibromomethane; and difunctionaltin halides such as tin dichloride, monomethyltin dichloride,dimethyltin dichloride, monoethyltin dichloride, diethyltin dichloride,monobutyltin dichloride, and dibutyltin dichloride.

Examples of trifunctional coupling agents include trifunctionalhaloalkanes such as trichloroethane and trichloropropane; trifunctionalhalosilanes such as methyltrichlorosilane and ethyltrichlorosilane; andtrifunctional alkoxysilanes such as methyltrimethoxysilane,phenyltrimethoxysilane, and phenyltriethoxysilane.

Examples of tetrafunctional coupling agents include tetrafunctionalhaloalkanes such as carbon tetrachloride, carbon tetrabromide, andtetrachloroethane; tetrafunctional halosilanes such as tetrachlorosilaneand tetrabromosilane; tetrafunctional alkoxysilanes such astetramethoxysilane and tetraethoxysilane; and tetrafunctional tinhalides such as tin tetrachloride and tin tetrabromide.

Examples of coupling agents having a functionality of 5 or higherinclude 1,1,1,2,2-pentachloroethane, perchloroethane,pentachlorobenzene, perchlorobenzene, octabromodiphenyl ether, anddecabromodiphenyl ether.

One of these coupling agents may be used individually, or two or more ofthese coupling agents may be used in combination.

Of these coupling agents, dichlorodimethylsilane is preferable from aviewpoint that a block copolymer having a diblock content within aspecific range can easily be produced. Note that through the couplingreaction using a coupling agent, a coupling moiety derived from thecoupling agent is introduced into a polymer chain (for example, atriblock structure) of the block copolymer.

In a case in which a particulate polymer A including a graft portion isproduced, examples of methods by which the graft portion may be graftedwith respect to a block copolymer that becomes a trunk portion include,but are not specifically limited to, a method in which polymerization ofa monomer composition containing monomers such as previously describedis carried out on a block copolymer that becomes a trunk portion and amethod in which a macromer obtained through polymerization of a monomercomposition containing monomers such as previously described is causedto bond to a polymer that becomes trunk portion.

In a case in which the particulate polymer A, a polymer that becomes atrunk portion thereof, or the like is produced through artificialpolymerization of a monomer composition, the proportion constituted byeach monomer in the monomer composition is normally the same as theproportion constituted by each monomer unit in the target polymer. Nospecific limitations are placed on the method of polymerization of thesepolymers. For example, any of solution polymerization, suspensionpolymerization, bulk polymerization, and emulsion polymerization may beadopted. Moreover, the polymerization reaction may be additionpolymerization such as ionic polymerization, radical polymerization, orliving radical polymerization. An emulsifier, dispersant, polymerizationinitiator, polymerization aid, or the like used in polymerization may bethe same as typically used and the amount thereof may also be the sameas typically used.

Although no specific limitations are placed on the method ofemulsification of the block copolymer, a method involvingphase-inversion emulsification of a preliminary mixture of a solution ofthe block copolymer obtained as described above and an aqueous solutionof an emulsifier is preferable. The phase-inversion emulsification canbe carried out, for example, using a known emulsifier and a knownemulsifying and dispersing device.

A water dispersion of the particulate polymer A can then be obtained by,as necessary, using a known method to remove organic solvent from theemulsion that is obtained after phase-inversion emulsification.

<Particulate Polymer B>

In an electrode produced by forming an electrode mixed material layer ona current collector using a slurry composition for a non-aqueoussecondary battery electrode that is produced using the bindercomposition, the particulate polymer B holds components contained in theelectrode mixed material layer to prevent these components detachingfrom the electrode mixed material layer (i.e., the particulate polymer Bfunctions as a binder in conjunction with the particulate polymer A setforth above). The particulate polymer B is in the form ofwater-insoluble particles.

<<Structure and Chemical Composition>>

The particulate polymer B is a random copolymer including a(meth)acrylic acid ester monomer unit in a proportion of not less than20.0 mass % and not more than 80.0 mass %. The particulate polymer B isa polymer that itself has high flexibility and that can improvestability of a slurry composition containing the binder composition as aresult of enabling good dispersion of solid content in a dispersionmedium such as water. Note that the particulate polymer B can includeother monomer units besides the (meth)acrylic acid ester monomer unit.Moreover, the particulate polymer B is a random copolymer in which morethan 90% is composed by a random region.

[(Meth)Acrylic Acid Ester Monomer Unit]

Examples of (meth)acrylic acid ester monomers that can form the(meth)acrylic acid ester monomer unit of the particulate polymer Binclude, but are not specifically limited to, the same (meth)acrylicacid ester monomers as can be used in formation of the graft portion ofthe particulate polymer A. Of these (meth)acrylic acid ester monomers,2-ethylhexyl (meth)acrylate and n-butyl (meth)acrylate are preferable,and 2-ethylhexyl acrylate is more preferable.

The proportion constituted by the (meth)acrylic acid ester monomer unitin the particulate polymer B when the amount of all repeating units inthe particulate polymer B is taken to be 100 mass % is required to benot less than 20.0 mass % and not more than 80.0 mass %, is preferably25.0 mass % or more, and more preferably 30.0 mass % or more, and ispreferably 77.5 mass % or less, more preferably 75.0 mass % or less, andeven more preferably 72.5 mass % or less. When the proportionconstituted by the (meth)acrylic acid ester monomer unit in theparticulate polymer B is not less than any of the lower limits set forthabove, low-temperature output characteristics of an obtained secondarybattery can be improved through a suitable increase in the degree ofswelling. Moreover, when the proportion constituted by the (meth)acrylicacid ester monomer unit in the particulate polymer B is not less thanany of the lower limits set forth above, solid content dispersingability that can be displayed by the particulate polymer B in a slurryincreases, and, as a result, electrolyte solution injectability of anelectrode obtained using the slurry composition can be improved.Furthermore, when the proportion constituted by the (meth)acrylic acidester monomer unit in the particulate polymer B is not more than any ofthe upper limits set forth above, an excessive decrease in closeadherence between an obtained electrode and another battery componentsuch as a separator can be inhibited, and, as a result, cyclecharacteristics of an obtained secondary battery can be improved.

[Other Monomer Units]

—Aromatic Vinyl Monomer Unit and Vinyl Cyanide Monomer Unit—

The particulate polymer B preferably further includes a monomer unitselected from an aromatic vinyl monomer unit and a vinyl cyanide monomerunit in addition to the (meth)acrylic acid ester monomer unit.

Examples of aromatic vinyl monomers that can be used to form thearomatic vinyl monomer unit include the same monomers as can be used information of the aromatic vinyl block region of the particulate polymerA. One of these aromatic vinyl monomers may be used individually, or twoor more of these aromatic vinyl monomers may be used in combination. Ofthese aromatic vinyl monomers, styrene is preferable.

Examples of vinyl cyanide monomers that can be used to form the vinylcyanide monomer unit include acrylonitrile, methacrylonitrile,a-chloroacrylonitrile, and a-ethylacrylonitrile. One of these vinylcyanide monomers may be used individually, or two or more of these vinylcyanide monomers may be used in combination. Of these vinyl cyanidemonomers, acrylonitrile and methacrylonitrile are preferable.

In a case in which the particulate polymer B includes a monomer unitselected from an aromatic vinyl monomer unit and a vinyl cyanide monomerunit, the proportion in which the monomer unit is included in theparticulate polymer B when all repeating units included in theparticulate polymer B are taken to be 100 mass % is preferably 10.0 mass% or more, more preferably 15.0 mass % or more, and even more preferably20.0 mass % or more, and is preferably 70.0 mass % or less, morepreferably 65.0 mass % or less, and even more preferably 60.0 mass % orless. Note that in a case in which the particulate polymer B includesonly one out of an aromatic vinyl monomer unit and a vinyl cyanidemonomer unit, the proportion in which that monomer unit is includedpreferably satisfies any of the ranges set forth above, and in a case inwhich the particulate polymer B includes both an aromatic vinyl monomerunit and a vinyl cyanide monomer unit, the total amount of both types ofmonomer units preferably satisfies any of the ranges set forth above.When the proportion in which a monomer unit selected from an aromaticvinyl monomer unit and a vinyl cyanide monomer unit is included in theparticulate polymer B is not less than any of the lower limits set forthabove, close adherence between an electrode and another batterycomponent such as a separator can be increased, and, as a result, cyclecharacteristics of an obtained secondary battery can be enhanced.Moreover, when the proportion in which a monomer unit selected from anaromatic vinyl monomer unit and a vinyl cyanide monomer unit is includedin the particulate polymer B is not more than any of the upper limitsset forth above, an excessive decrease in flexibility of an obtainedelectrode can be inhibited, and, as a result, cycle characteristics ofan obtained secondary battery can be enhanced.

—Acidic Group-Containing Monomer Unit—

The particulate polymer B preferably further includes an acidicgroup-containing monomer unit. Examples of acidic group-containingmonomers that can be used to form the acidic group-containing monomerunit include the same acidic group-containing monomers as can be used toform the graft portion of the previously described particulate polymerA. One of these acidic group-containing monomers may be usedindividually, or two or more of these acidic group-containing monomersmay be used in combination. Of these acidic group-containing monomers,(meth)acrylic acid and itaconic acid are preferable.

In a case in which the particulate polymer B includes an acidicgroup-containing monomer unit, the proportion in which the acidicgroup-containing monomer unit is included in the particulate polymer Bwhen all repeating units included in the particulate polymer B are takento be 100 mass % is preferably 1.0 mass % or more, more preferably 1.5mass % or more, and even more preferably 2.0 mass % or more, and ispreferably 15.0 mass % or less, more preferably 10.0 mass % or less, andeven more preferably 8.0 mass % or less. When the proportion constitutedby the acidic group-containing monomer unit is not less than any of thelower limits set forth above, slurry stability can be increased, and, asa result, low-temperature output characteristics of a secondary batteryincluding an obtained electrode can be improved. Moreover, when theproportion constituted by the acidic group-containing monomer unit isnot less than any of the lower limits set forth above, affinity withelectrolyte solution of an electrode that can be formed using a slurrycomposition containing the binder composition can be improved, and thusa secondary battery having good electrolyte solution injectability canbe formed. Furthermore, when the proportion constituted by the acidicgroup-containing monomer unit is not more than any of the upper limitsset forth above, an obtained electrode can be provided with higheradhesiveness to another battery component such as a separator, and, as aresult, swelling of the electrode accompanying repeated charging anddischarging can be effectively inhibited.

—Others—

Besides the monomer units set forth above, the particulate polymer B mayinclude any monomer unit that is copolymerizable with various monomerunits such as set forth above. Examples of such monomer units includeethylenically unsaturated carboxylic acid ester monomers andcross-linkable monomers. One of these may be used individually, or twoor more of these may be used in combination.

The ethylenically unsaturated carboxylic acid ester monomer may, forexample, be an ethylenically unsaturated carboxylic acid ester monomerthat includes a polar group. Examples of polar group-containingethylenically unsaturated carboxylic acid ester monomers includehydroxyalkyl esters of (meth)acrylic acid and glycidyl (meth)acrylate.Examples of hydroxyalkyl esters of (meth)acrylic acid include2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. Ofthese examples, 2-hydroxyethyl (meth)acrylate is preferable.

Examples of cross-linkable monomers that can be used include monomersthat display cross-linkability such as divinylbenzene, allyl glycidylether, allyl methacrylate, and N-methylolacrylamide.

[Volume-Average Particle Diameter]

The volume-average particle diameter of the particulate polymer B ispreferably 0.01 μm or more, more preferably 0.03 μm or more, and evenmore preferably 0.05 μm or more, and is preferably 1.00 μm or less, morepreferably 0.80 μm or less, and even more preferably 0.50 μm or less.When the volume-average particle diameter of the particulate polymer Bis not less than any of the lower limits set forth above, closeadherence between an electrode and another battery component such as aseparator can be increased, and electrode swelling accompanying chargingand discharging can be effectively inhibited. Moreover, when thevolume-average particle diameter of the particulate polymer B is notmore than any of the upper limits set forth above, an excessive decreasein specific surface area of the particulate polymer B can be inhibited,adhesive ability that can be displayed by the particulate polymer B canbe sufficiently increased, and, as a result, cycle characteristics of anobtained secondary battery can be improved.

Note that the volume-average particle diameter of the particulatepolymer B can be measured by a method described in the EXAMPLES sectionof the present specification.

<Content Ratio of Particulate Polymer A and Particulate Polymer B>

The content of the particulate polymer A in the presently disclosedbinder composition when the total content of the particulate polymer Aand the particulate polymer B is taken to be 100 mass % is preferably 20mass % or more, more preferably 25 mass % or more, and even morepreferably 30 mass % or more, and is preferably 80 mass % or less, morepreferably 75 mass % or less, and even more preferably 70 mass % orless. When the content ratio of the particulate polymer A is not lessthan any of the lower limits set forth above, cycle characteristics ofan obtained secondary battery can be improved. Moreover, when thecontent ratio of the particulate polymer A is not more than any of theupper limits set forth above, low-temperature output characteristics ofan obtained secondary battery can be enhanced. Furthermore, when thecontent ratio of the particulate polymer A is not more than any of theupper limits set forth above (i.e., when the particulate polymer B isused in combination therewith in at least a certain ratio),dispersibility of solid content such as an electrode active material ina slurry can be improved, an electrode having high electrode activematerial density can be well formed, and electrolyte solutioninjectability with respect to an obtained secondary battery can beimproved.

<Solvent>

The presently disclosed binder composition can further contain a solventsuch as water. Examples of solvents that can be used include water, anaqueous solution containing water, and a mixed solution of water and asmall amount of an organic solvent. Of these solvents, water ispreferable.

<Other Components>

The presently disclosed binder composition can contain components otherthan those described above (i.e., other components). For example, thebinder composition may contain a known particulate binder (for example,a styrene-butadiene random copolymer) other than the particulate polymerA and the particulate polymer B set forth above. In a case in which thebinder composition contains a known particulate binder other than theparticulate polymer A and the particulate polymer B, the content of thisparticulate polymer is required to be less than the content of theparticulate polymer A and the content of the particulate polymer B, andis preferably 10 mass % or less of the total content of the particulatepolymer A and the particulate polymer B.

The binder composition may also contain known additives. Examples ofsuch known additives include antioxidants such as2,6-di-tert-butyl-p-cresol, defoamers, and dispersants. One othercomponent may be used individually, or two or more other components maybe used in combination in a freely selected ratio.

<Production Method of Binder Composition>

The presently disclosed binder composition can be produced, without anyspecific limitations, by mixing the particulate polymer A, theparticulate polymer B, and optionally used other components in thepresence of a solvent such as water. Note that in a case in whichdispersion liquids of the particulate polymer A and the particulatepolymer B are used in production of the binder composition, liquidcontent of these dispersion liquids may be used as the solvent of thebinder composition.

(Slurry Composition for Non-Aqueous Secondary Battery Electrode)

The presently disclosed slurry composition for a non-aqueous secondarybattery electrode contains an electrode active material and thepresently disclosed binder composition for a non-aqueous secondarybattery electrode set forth above, and may optionally further containother components. In other words, the presently disclosed slurrycomposition for a non-aqueous secondary battery electrode normallycontains an electrode active material, the previously describedparticulate polymers A and B, and the previously described solvent, andmay optionally further contain other components. When the presentlydisclosed slurry composition for a non-aqueous secondary batteryelectrode is used to form an electrode mixed material layer of anelectrode, the electrode active material can be well dispersed and anelectrode mixed material layer having comparatively high density can bewell formed as a result of the presently disclosed slurry compositionfor a non-aqueous secondary battery electrode containing the bindercomposition set forth above. Consequently, a non-aqueous secondarybattery can be caused to display excellent battery characteristics, andparticularly low-temperature cycle characteristics and low-temperatureoutput characteristics, by using an electrode formed using the presentlydisclosed slurry composition for a non-aqueous secondary batteryelectrode.

Although the following describes, as one example, a case in which theslurry composition for a non-aqueous secondary battery electrode is aslurry composition for a lithium ion secondary battery negativeelectrode, the presently disclosed slurry composition for a non-aqueoussecondary battery electrode is not limited to the following example.

<Electrode Active Material>

The electrode active material is a material that gives and receiveselectrons in an electrode of a secondary battery. The negative electrodeactive material of a lithium ion secondary battery is normally amaterial that can occlude and release lithium.

More specifically, the negative electrode active material of a lithiumion secondary battery may, for example, be a carbon-based negativeelectrode active material, a metal-based negative electrode activematerial, or a negative electrode active material that is a combinationthereof.

Examples of carbonaceous materials include graphitizing carbon andnon-graphitizing carbon, typified by glassy carbon, which has astructure similar to an amorphous structure.

Examples of the graphitizing carbon include carbon materials made fromtar pitch obtained from petroleum or coal. Specific examples includecoke, meso-carbon microbeads (MCMB), mesophase pitch-based carbon fiber,and pyrolytic vapor-grown carbon fiber.

Examples of the non-graphitizing carbon include pyrolyzed phenolicresin, polyacrylonitrile-based carbon fiber, quasi-isotropic carbon,pyrolyzed furfuryl alcohol resin (PFA), and hard carbon.

Examples of graphitic materials include natural graphite and artificialgraphite.

Examples of the artificial graphite include artificial graphite obtainedby heat-treating carbon containing graphitizing carbon mainly at 2800°C. or higher, graphitized MCMB obtained by heat-treating MCMB at 2000°C. or higher, and graphitized mesophase pitch-based carbon fiberobtained by heat-treating mesophase pitch-based carbon fiber at 2000° C.or higher.

The metal-based negative electrode active material is an active materialthat contains metal, the structure of which usually contains an elementthat allows insertion of lithium, and that has a theoretical electriccapacity per unit mass of 500 mAh/g or more when lithium is inserted.Examples of metal-based active materials that can be used includelithium metal, simple substances of metals that can form a lithium alloy(for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr,Zn, and Ti) and alloys thereof, and oxides, sulfides, nitrides,silicides, carbides, and phosphides of any of the preceding examples. Ofthese metal-based negative electrode active materials, active materialscontaining silicon (silicon-based negative electrode active materials)are preferred. One reason for this is that the capacity of a lithium ionsecondary battery can be increased through use of a silicon-basednegative electrode active material.

Examples of silicon-based negative electrode active materials includesilicon (Si), silicon-containing alloys, SiO, SiO_(x), and a compositeof a Si-containing material and conductive carbon obtained by coating orcompositing the Si-containing material with the conductive carbon. Oneof these silicon-based negative electrode active materials may be usedindividually, or two or more of these silicon-based negative electrodeactive materials may be used in combination.

<Other Components>

Examples of other components that may be contained in the slurrycomposition include, but are not specifically limited to, the same othercomponents as may be contained in the presently disclosed bindercomposition. One of such other components may be used individually, ortwo or more of such other components may be used in combination in afreely selected ratio.

<Production of Slurry Composition for Non-Aqueous Secondary BatteryElectrode>

The slurry composition set forth above can be produced by dispersing ordissolving the components described above in a solvent such as water.Specifically, the slurry composition can be produced by mixing theabove-described components and the solvent using a mixer such as a ballmill, a sand mill, a bead mill, a pigment disperser, a grinding machine,an ultrasonic disperser, a homogenizer, a planetary mixer, or a FILMIX.Mixing of the above-described components and the solvent can normally beperformed for 10 minutes to several hours in a temperature range of roomtemperature to 80° C. In production of the slurry composition, theamount of the binder composition, in terms of solid content, can be setas not less than 0.5 parts by mass and not more than 15 parts by massper 100 parts by mass of the electrode active material. The solvent usedin production of the slurry composition can be any of the same types asfor the binder composition. Moreover, the solvent used in production ofthe slurry composition can contain solvent that was contained in thebinder composition.

(Electrode for Non-Aqueous Secondary Battery)

The presently disclosed electrode for a non-aqueous secondary batteryincludes an electrode mixed material layer formed using the slurrycomposition for a non-aqueous secondary battery electrode set forthabove, and normally includes a substrate such as a current collector andan electrode mixed material layer of 1.70 g/cm³ or more in density thatis formed on the substrate. The electrode mixed material layer containsat least an electrode active material and the previously describedparticulate polymers A and B. It should be noted that componentscontained in the electrode mixed material layer are components that werecontained in the slurry composition for a non-aqueous secondary batteryelectrode. Furthermore, the preferred ratio of these components in theelectrode mixed material layer is the same as the preferred ratio ofthese components in the slurry composition.

The presently disclosed electrode for a non-aqueous secondary battery isan electrode that is formed using a slurry composition containing thepresently disclosed binder composition for a non-aqueous secondarybattery electrode. Consequently, the presently disclosed electrode for anon-aqueous secondary battery is a high-density electrode having adensity of 1.70 g/cm³ or more that can enhance low-temperature outputcharacteristics and cycle characteristics of a secondary battery. Thedensity of the electrode for a non-aqueous secondary battery ispreferably 1.72 g/cm³ or more. When the density is not less than any ofthe lower limits set forth above, a secondary battery including theelectrode can be provided with an even higher capacity than conventionalsecondary batteries.

<Formation of Electrode for Non-Aqueous Secondary Battery>

The presently disclosed electrode for a non-aqueous secondary batterycan be produced, for example, through a step of applying the previouslydescribed slurry composition onto a substrate such as a currentcollector (application step) and a step of drying the slurry compositionthat has been applied onto the substrate to form an electrode mixedmaterial layer on the substrate (drying step).

[Application Step]

The slurry composition can be applied onto the substrate by any commonlyknown method without any specific limitations. Specific examples ofapplication methods that can be used include doctor blading, dipcoating, reverse roll coating, direct roll coating, gravure coating,extrusion coating, and brush coating. During application, the slurrycomposition may be applied onto one side or both sides of the substrate.The thickness of the slurry coating on the substrate after applicationbut before drying may be set as appropriate in accordance with thethickness of the electrode mixed material layer that is to be obtainedafter drying.

[Drying Step]

The slurry composition on the substrate may be dried by any commonlyknown method without any specific limitations. Examples of dryingmethods that can be used include drying by warm, hot, or low-humidityair; drying in a vacuum; and drying by irradiation with infrared light,electron beams, or the like. Drying of the slurry composition on thesubstrate in this manner forms an electrode mixed material layer on thesubstrate and thereby provides an electrode for a secondary battery thatincludes the substrate and the electrode mixed material layer.

After the drying step, the electrode mixed material layer is preferablyfurther subjected to a pressing process by mold pressing, roll pressing,or the like. The pressing process can improve close adherence of theelectrode mixed material layer and the substrate and can increase thedensity of the electrode mixed material layer. In particular, thepresently disclosed slurry composition set forth above is suitable forformation of an electrode mixed material layer that is densified by apressing process due to the suitable degree of flexibility and goodsolid content dispersing ability that can be displayed by theparticulate polymer B contained therein. Moreover, an electrode formedusing the presently disclosed slurry composition has high affinity withelectrolyte solution. Therefore, the presently disclosed electrodeformed using this slurry composition has high electrolyte solutioninjectability during secondary battery production while also having ahigh density of 1.70 g/cm³ or more.

Note that in a case in which the electrode mixed material layer containsa curable polymer, the polymer is preferably cured after formation ofthe electrode mixed material layer.

(Non-Aqueous Secondary Battery)

The presently disclosed non-aqueous secondary battery includes apositive electrode, a negative electrode, an electrolyte solution, and aseparator, wherein the presently disclosed electrode for a non-aqueoussecondary battery is used as at least one of the positive electrode andthe negative electrode. The presently disclosed non-aqueous secondarybattery has excellent battery characteristics such as low-temperatureoutput characteristics and cycle characteristics as a result ofincluding the presently disclosed electrode for a non-aqueous secondarybattery.

Although the following describes, as one example, a case in which thesecondary battery is a lithium ion secondary battery, the presentlydisclosed secondary battery is not limited to the following example.

<Electrodes>

As described above, the presently disclosed electrode for a non-aqueoussecondary battery is used as at least one of the positive electrode andthe negative electrode. In other words, the positive electrode of thelithium ion secondary battery may be the presently disclosed electrodeand the negative electrode of the lithium ion secondary battery may be aknown negative electrode other than the presently disclosed electrode.Alternatively, the negative electrode of the lithium ion secondarybattery may be the presently disclosed electrode and the positiveelectrode of the lithium ion secondary battery may be a known positiveelectrode other than the presently disclosed electrode. Furtheralternatively, the positive electrode and the negative electrode of thelithium ion secondary battery may both be the presently disclosedelectrode. In particular, it is preferable that at least the negativeelectrode is the presently disclosed electrode for a non-aqueoussecondary battery.

Note that when a known electrode other than the presently disclosedelectrode for a non-aqueous secondary battery is used, this electrodemay be an electrode that is obtained by forming an electrode mixedmaterial layer on a substrate such as a current collector by a knownproduction method.

<Electrolyte Solution>

The electrolyte solution is normally an organic electrolyte solutionobtained by dissolving a supporting electrolyte in an organic solvent.The supporting electrolyte of a lithium ion secondary battery may, forexample, be a lithium salt. Examples of lithium salts that can be usedinclude LiPF₆, LiAsF₆, LiBF₄, LiSbF₆, LiAlCl₄, LiClO₄, CF₃SO₃Li,C₄F₉SO₃Li, CF₃COOLi, (CF₃CO)₂NLi, (CF₃SO₂)₂NLi, and (C₂F₅SO₂)NLi. Ofthese lithium salts, LiPF₆, LiClO₄, and CF₃SO₃Li are preferable, andLiPF₆ is particularly preferable as these lithium salts readily dissolvein solvents and exhibit a high degree of dissociation. One electrolytemay be used individually, or two or more electrolytes may be used incombination in a freely selected ratio. In general, lithium ionconductivity tends to increase when a supporting electrolyte having ahigh degree of dissociation is used. Therefore, lithium ion conductivitycan be adjusted through the type of supporting electrolyte that is used.

The organic solvent used in the electrolyte solution is not specificallylimited so long as the supporting electrolyte can dissolve therein.Suitable examples include carbonates such as dimethyl carbonate (DMC),ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate(PC), butylene carbonate (BC), and ethyl methyl carbonate (EMC); esterssuch as γ-butyrolactone and methyl formate; ethers such as1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compoundssuch as sulfolane and dimethyl sulfoxide. Furthermore, a mixture of suchsolvents may be used. Of these solvents, carbonates are preferred fortheir high dielectric constant and broad stable potential region.

The concentration of the electrolyte in the electrolyte solution can beadjusted as appropriate and is, for example, preferably 0.5 mass % to 15mass %, more preferably 2 mass % to 13 mass %, and even more preferably5 mass % to 10 mass %. Known additives such as vinylene carbonate (VC),fluoroethylene carbonate, and ethyl methyl sulfone can be added to theelectrolyte solution.

<Separator>

The separator may be a separator such as described in JP 2012-204303 A,for example, but is not specifically limited thereto. Of theseseparators, a microporous membrane made of polyolefinic (polyethylene,polypropylene, polybutene, or polyvinyl chloride) resin is preferredbecause such a membrane can reduce the total thickness of the separator,which increases the ratio of electrode active material in the secondarybattery, and consequently increases the capacity per volume.

<Production of Non-Aqueous Secondary Battery>

The presently disclosed non-aqueous secondary battery can be producedby, for example, stacking the positive electrode and the negativeelectrode with the separator in-between, performing rolling, folding, orthe like of the resultant stack as necessary in accordance with thebattery shape, placing the stack in a battery container, injecting theelectrolyte solution into the battery container, and sealing the batterycontainer. In order to prevent pressure increase inside the secondarybattery and occurrence of overcharging or overdischarging, anovercurrent preventing device such as a fuse or a PTC device; anexpanded metal; or a lead plate may be provided as necessary. The shapeof the secondary battery may be a coin type, button type, sheet type,cylinder type, prismatic type, flat type, or the like.

EXAMPLES

The following provides a more specific description of the presentdisclosure based on examples. However, the present disclosure is notlimited to the following examples. In the following description, “%” and“parts” used in expressing quantities are by mass, unless otherwisespecified.

Moreover, in the case of a polymer that is produced throughpolymerization of a plurality of types of monomers, the proportion inthe polymer constituted by a monomer unit that is formed throughpolymerization of a given monomer is normally, unless otherwisespecified, the same as the ratio (charging ratio) of the given monomeramong all monomers used in polymerization of the polymer.

In the examples and comparative examples, the proportion in aparticulate polymer A constituted by an acidic group-containing monomerunit included in a graft portion was evaluated as described below.

Moreover, the following methods were used in the examples andcomparative examples to measure the volume-average particle diameter ofparticulate polymers A and B, the diblock content of a particulatepolymer A, and the content ratio of particulate polymers A and B.

Furthermore, the following methods were used in the examples andcomparative examples to evaluate the stability of a slurry composition(slurry stability), the swelling and electrolyte solution injectabilityof an electrode, and the low-temperature output characteristics andcycle characteristics of a secondary battery.

<Proportion in Particulate Polymer A Constituted by AcidicGroup-Containing Monomer Unit Included in Graft Portion>

For a particulate polymer A produced in each of Examples 1 to 9 and 11to 17, and Comparative Examples 1 and 3 to 5, the proportion in theoverall particulate polymer A constituted by an acidic group-containingmonomer unit included in a graft portion was determined by performingcentrifugal separation of a water dispersion present after a graftingreaction to remove acidic group-containing monomer that had notundergone grafting reaction, subsequently measuring the surface acidcontent of the particulate polymer A, and then determining theaforementioned proportion based on the measured surface acid content.

<Volume-Average Particle Diameter of Particulate Polymers A and B>

The volume-average particle diameter D50 of each particulate polymer Aor B produced in the examples and comparative examples was determined asa particle diameter (μm) at which, in a particle size distribution(volume basis) measured by a laser diffraction particle diameterdistribution analyzer (produced by Beckman Coulter, Inc.; product name:LS-230) with respect to a water dispersion adjusted to a solid contentconcentration of 0.1 mass %, cumulative volume calculated from a smalldiameter end of the distribution reached 50%.

<Diblock Content of Particulate Polymer A>

The diblock content of a particulate polymer A was calculated based onpolystyrene-equivalent molecular weight obtained by high-performanceliquid chromatography (apparatus: HLC8220 (model no.) produced by TosohCorporation). Moreover, in the high-performance liquid chromatography,three linked columns (Shodex KF-404HQ (model no.) produced by ShowaDenko K. K.; column temperature: 40° C.; carrier: tetrahydrofuran atflow rate of 0.35 mL/min) were used, and a differential refractometerand a UV detector were used as detectors. Molecular weight calibrationwas performed by 12 points for standard polystyrene (produced by PolymerLaboratories Ltd.; standard molecular weight: 500 to 3,000,000). In achart obtained by the high-performance liquid chromatography, thediblock content (mass %) was calculated based on the area proportionconstituted by the area of peaks corresponding to polymer chains thatwere diblock structures relative to the overall chart.

<Content Ratio of Particulate Polymers A and B in Binder Composition>

A binder composition produced in each example or comparative example wasdried in the form of a film to obtain a test specimen. The test specimenwas sectioned by a standard method and then the sectioned surface wasobserved using an atomic force microscope (unit: SPA400; probe station:SPI3800N; cantilever: SI-DF40; measurement mode: SIS-DFM). A squareregion having a side length of 3μm was arbitrarily selected in thesectioned surface of the test specimen observed using the atomic forcemicroscope, and a viscoelasticity distribution was measured to performmapping. Based on the mapping results, the area ratio of regionsdisplaying viscoelasticities corresponding respectively to theparticulate polymers A and B was calculated, and thus a content ratio(mass basis) of the particulate polymers A and B was measured.

<Slurry Stability>

Various components were prepared in the same way as in production of aslurry composition for a non-aqueous secondary battery negativeelectrode in each example or comparative example. A mixture was thenobtained in the same way as in each example or comparative example byadding 100 parts of artificial graphite (capacity: 360 mAh/g) as anegative electrode active material, 1 part of carbon black (produced byTIMCAL; product name: Super C65) as a conductive material, and 1.2 partsin terms of solid content of a 2% aqueous solution of carboxymethylcellulose (produced by Nippon Paper Industries Co., Ltd.; product name:MAC-350HC) as a thickener into a planetary mixer equipped with a disperblade. The resultant mixture was adjusted to a solid contentconcentration of 60% with deionized water and was subsequently mixed at25° C. for 60 minutes. Next, the mixture was adjusted to a solid contentconcentration of 52% with deionized water and was then further mixed at25° C. for 15 minutes to obtain a mixed liquid. The viscosity MO (mPa·s)of this mixed liquid was measured using a B-type viscometer (produced byToki Sangyo Co., Ltd.; product name: TV-25) under measurement conditionsof a measurement temperature of 25° C., a No. 4 measurement rotor, and arotor rotation speed of 60 rpm.

On the other hand, 2.0 parts in terms of solid content of a bindercomposition having the same chemical composition as that produced ineach example or comparative example was added to a mixed liquid havingthe same chemical composition as the mixed liquid for which theviscosity M0 was measured so as to obtain a solution for measurement ofviscosity M1. The solution for measurement of viscosity M1 was loadedinto a vessel having a diameter of 5.5 cm and a height of 8.0 cm and wasstirred at a rotation speed of 3,000 rpm for 10 minutes using a TK HomoDisper (produced by PRIMIX Corporation; disper blade diameter: 40 mm).After stirring, the viscosity M1 (mPa·s) of the slurry composition wasmeasured. The stability of the slurry composition was calculated asΔM=M1/M0 (times) and then slurry stability was evaluated by thefollowing standard. A smaller value indicates that the slurrycomposition has higher stability.

A: ΔM≤1.0 times

B: 1.0 times<ΔM<1.2 times

C: 1.2 times≤ΔM

<Electrode Swelling>

After 100 cycles of repeated charging and discharging, a secondarybattery was charged at 1C in a 25° C. environment. The secondary batterywas dismantled in a charged state to remove the negative electrode, andthe thickness (d2) of the negative electrode (excluding the thickness ofthe current collector) was measured. The rate of change relative to thethickness (d0) of the negative electrode (excluding the thickness of thecurrent collector) before production of the lithium ion secondarybattery (electrode swelling={(d2−d0)/d0}×100(%)) was calculated and wasjudged by the following standard. A smaller rate of change indicatesless swelling of the negative electrode after cycling.

A: Rate of change of less than 25%

B: Rate of change of not less than 25% and less than 30%

C: Rate of change of not less than 30% and less than 35%

D: Rate of change of 35% or more

<Electrolyte Solution Injectability>

The negative electrode mixed material layer side of a negative electrodeweb produced in each example or comparative example was roll pressedwith a line pressure of 14 t (tons) in an environment having atemperature of 25±3° C. to adjust the electrode mixed material layerdensity to 1.75 g/cm³. A circle of 16 mm in diameter was cut out fromthe produced negative electrode for a secondary battery and then 1 μL ofpropylene carbonate (reagent produced by Kishida Chemical Co., Ltd.) wasdripped onto the surface at which the negative electrode mixed materiallayer was located. The time taken for the droplet of propylene carbonateon the negative electrode to penetrate into the negative electrode mixedmaterial layer after dripping (penetration time) was measured by eye andwas evaluated by the following standard. A shorter penetration timeindicates better affinity between the negative electrode and propylenecarbonate contained in a typical electrolyte solution, and thusindicates better electrolyte solution injectability during secondarybattery production.

A: Penetration time of less than 110 s

B: Penetration time of not less than 110 s and less than 130 s

C: Penetration time of not less than 130 s and less than 150 s

D: Penetration time of 150 s or more

<Low-Temperature Output Characteristics>

A secondary battery produced in each example or comparative example wasleft at rest in a 25° C. environment for 24 hours. The initial capacityof the secondary battery was subsequently checked. The secondary batterywas fully charged to 4.35 V by CC-CV charging (cut-off condition of0.02C) at 25° C. and was then CC discharged to 3.0 V at 0.2C in a −10°C. environment. The discharge capacity Cl in this discharging wasobtained. The secondary battery was fully charged to 4.35 V once againby CC-CV charging (cut-off condition of 0.02C) at 25° C. and was then CCdischarged to 3.0 V at 1C in a −10° C. environment. The dischargecapacity C2 in this discharging was obtained. A capacity maintenancerate ΔC(=(C2/C1)×100) was calculated based on the values of C1 and C2obtained as described above and was evaluated by the following standard.A larger value for C2/C1 indicates that the lithium ion secondarybattery has better low-temperature output characteristics.

A: 55% or more

B: More than 50% and less than 55%

C: More than 45% and not more than 50%

D: 45% or less

<Cycle Characteristics>

A secondary battery produced in each example or comparative example wasleft at rest in a 25° C. environment for 24 hours. The secondary batterywas subjected to a charge/discharge operation of charging to 4.35 V at1C and discharging to 3.0 V at 1C in a 25° C. environment, and theinitial capacity C′0 was measured. In addition, the secondary batterywas CC-CV charged (upper limit cell voltage of 4.35 V) by a 1Cconstant-current method and was CC discharged to a cell voltage of 3.00V by a 1C constant-current method in a 45° C. environment. This chargingand discharging was repeated, and the capacity C′1 after 300 cycles wasmeasured. High-temperature cycle characteristics were evaluated as acapacity maintenance rate expressed by ΔC′=C′1/C′0×100(%). A highervalue indicates better cycle characteristics.

A: AC′≥80%

B: 75%≤ΔC′<80%

C: 70%≤ΔC′<75%

D: ΔC′<70%

Example 1

<Production of particulate Polymer A>

<<Block Copolymer Solution Production Step>>

A pressure-resistant reactor was charged with 233.3 kg of cyclohexane,60.0 mmol of N,N,N′,N′-tetramethylethylenediamine (hereinafter, referredto as TMEDA), and 24.7 kg of styrene as an aromatic vinyl monomer. Thesematerials were stirred at 40° C. while 2000.0 mmol of n-butyllithium wasadded thereto as a polymerization initiator, and were then heated to 50°C. while polymerization was carried out for 1 hour. The polymerizationconversion rate of styrene was 100%. Next, temperature control wasperformed to maintain a temperature of 50° C. to 60° C. whilecontinuously adding 78.3 kg of isoprene into the pressure-resistantreactor over 1 hour as an aliphatic conjugated diene monomer. Thepolymerization reaction was continued for 1 hour after completingaddition of the isoprene. The polymerization conversion rate of isoprenewas 100%.

Next, 820.0 mmol of dichlorodimethylsilane was added into thepressure-resistant reactor as a coupling agent and a coupling reactionwas performed for 2 hours to form a styrene-isoprene coupled blockcopolymer.

Thereafter, 4000.0 mmol of methanol was added to the reaction liquid inwhich styrene-isoprene block copolymer having active terminals wasthought to remain and was thoroughly mixed therewith to deactivateactive terminals. Next, 0.3 parts of 2,6-di-tert-butyl-p-cresol as anantioxidant was added to 100 parts of the reaction liquid obtained asdescribed above (containing 30.0 parts of polymer component) and wasmixed therewith to obtain a block copolymer solution. The obtained blockcopolymer had a styrene content of 24 mass %, a coupling rate of 82 mass%, and a weight-average molecular weight Mw of 140,000.

<<Emulsification Step>>

First, sodium linear alkylbenzene sulfonate was dissolved in deionizedwater to produce an aqueous solution having a total solid content of 2mass %.

A tank was charged with 500 g of the block copolymer solution obtainedin the block copolymer solution production step and 500 g of theproduced aqueous solution, and preliminary mixing of these materials wasperformed by stirring to obtain a preliminary mixture. Next, a meteringpump was used to transfer the preliminary mixture from the tank to acontinuous high-performance emulsifying and dispersing device (producedby Pacific Machinery & Engineering Co., Ltd.; product name: MilderMDN303V) at a rate of 100 g/min, and the preliminary mixture was stirredat a rotation speed of 20,000 rpm to cause phase-inversionemulsification of the preliminary mixture and obtain an emulsion.

Cyclohexane in the obtained emulsion was subsequently vacuum evaporatedin a rotary evaporator. Thereafter, the emulsion resulting from thisevaporation was left to separate for 1 day in a chromatographic columnequipped with a stop-cock, and a lower layer portion after separationwas removed to perform concentration.

Finally, an upper layer portion was filtered through a 100-mesh screento obtain a latex (solid content concentration: 40%) containing a blockcopolymer including a styrene region and an isoprene region.

<<Grafting Step>>

A vessel was charged with 20 parts of methacrylic acid as an acidicgroup-containing monomer, the block copolymer latex containing 97 partsin terms of solid content of the block copolymer, and deionized water inan amount such that the solid content concentration was 30%. Thesematerials were sufficiently stirred and then 0.6 parts oftetraethylenepentamine and 0.6 parts of t-butyl hydroperoxide were addedinto the vessel as polymerization initiators to initiate graftpolymerization. The graft polymerization reaction temperature wasmaintained at 30° C. At 1.0 hours after the start of graftpolymerization, the temperature was raised to 70° C. and was maintainedat 70° C. for 2 hours. Once a polymerization conversion rate of 97% ormore was confirmed, the graft polymerization reaction was terminated toyield a water dispersion (solid content concentration: 40%) containing aparticulate polymer A that was a block copolymer into which a graftportion composed by only acidic group-containing monomer units had beenintroduced. Note that the added methacrylic acid polymerized amongstitself to form a methacrylic acid polymer, and then part of themethacrylic acid polymer that was formed bonded to an aliphaticconjugated diene block region of the block copolymer to form a graftportion. On the other hand, methacrylic acid polymer that did not bondto the block copolymer was dispersed in the water dispersion. Therefore,for the purposes of use in the subsequently described steps, the waterdispersion containing the particulate polymer A that was obtained asdescribed above was subjected to centrifugal separation to removemethacrylic acid polymer that had not bonded to the block copolymer.

<Production of Particulate Polymer B>

A polymerization can A was charged with 83.7 parts of deionized water,0.2 parts of sodium dodecyl diphenyl ether sulfonate as an emulsifier,and 1.0 parts of ammonium persulfate as a polymerization initiator.These materials were heated to 70° C. and were stirred at a temperatureof 70° C. for 30 minutes.

Next, 64.1 parts of 2-ethylhexyl acrylate as a (meth)acrylic acid estermonomer, 30.0 parts of styrene as an aromatic vinyl monomer, 4.0 partsof acrylic acid as an acidic group-containing monomer, 1.7 parts ofallyl glycidyl ether as a cross-linkable monomer, 0.2 parts of ally!methacrylate as a cross-linkable monomer, 0.8 parts of sodium dodecyldiphenyl ether sulfonate as an emulsifier, and 74 parts of deionizedwater were added into a separate polymerization can B, and were stirredat a temperature of 25° C. to obtain an emulsion. The obtained emulsionwas consecutively added from the polymerization can B to thepolymerization can A over approximately 200 minutes. Thereafter,approximately 180 minutes of stirring was performed and then cooling wasperformed to terminate the polymerization reaction once thepolymerization conversion rate was 97% or more. Next, pH adjustment wasperformed using 4% sodium hydroxide aqueous solution and thermal-vacuumdistillation was performed to remove unreacted monomer and thereby yielda water dispersion containing a particulate polymer B that was a randomcopolymer including a (meth)acrylic acid ester monomer in a specificproportion.

<Production of Binder Composition for Non-Aqueous Secondary BatteryNegative Electrode Mixed Material Layer>

A mixture was obtained by loading the water dispersion of theparticulate polymer A obtained as described above and the waterdispersion of the particulate polymer B obtained as described above intoa vessel such that the mixing ratio of the particulate polymer A and theparticulate polymer B was 50:50 (mass basis). The obtained mixture wasstirred for 1 hour using a stirrer (produced by SHINTO Scientific Co.,Ltd.; product name: Three-One Motor) to obtain a binder composition fora negative electrode mixed material layer. When the content ratio of theparticulate polymer A and the particulate polymer B in the bindercomposition was verified by the previously described method, the contentratio was confirmed to be the same as the charging ratio.

<Production of Slurry Composition for Non-Aqueous Secondary BatteryNegative Electrode Mixed Material Layer>

A mixture was obtained by adding 100 parts of artificial graphite(capacity: 360 mAh/g) as a negative electrode active material, 1 part ofcarbon black (produced by TIMCAL; product name: Super C65) as aconductive material, and 1.2 parts in terms of solid content of a 2%aqueous solution of carboxymethyl cellulose (produced by Nippon PaperIndustries Co., Ltd.; product name: MAC-350HC) as a thickener into aplanetary mixer equipped with a disper blade. The resultant mixture wasadjusted to a solid content concentration of 60% with deionized waterand was subsequently mixed at 25° C. for 60 minutes. Next, the mixturewas adjusted to a solid content concentration of 52% with deionizedwater and was then further mixed at 25° C. for 15 minutes to obtain amixed liquid. Deionized water and 2.2 parts in terms of solid content ofthe binder composition produced as described above were added to theobtained mixed liquid, and the final solid content concentration wasadjusted to 48%. Further mixing was performed for 10 minutes and then adefoaming process was carried out under reduced pressure to yield aslurry composition for a negative electrode mixed material layer havinggood fluidity.

<Formation of Negative Electrode>

The obtained slurry composition for a negative electrode mixed materiallayer was applied onto copper foil (current collector) of 15 μm inthickness by a comma coater such as to have a thickness after drying ofapproximately 150 μm. The applied slurry composition was dried byconveying the copper foil inside a 60° C. oven for 2 minutes at a speedof 0.5 m/min. Thereafter, 2 minutes of heat treatment was performed at120° C. to obtain a negative electrode web.

The negative electrode web was rolled by roll pressing to obtain anegative electrode having a negative electrode mixed material layerthickness of 80 μm and a negative electrode mixed material layer densityof 1.75 g/cm³.

<Formation of Positive Electrode>

A slurry composition for a positive electrode mixed material layer wasobtained by combining 100 parts of LiCoO₂ having a volume-averageparticle diameter of 12 μm as a positive electrode active material, 2parts of acetylene black (produced by Denka Company Limited; productname: HS-100) as a conductive material, 2 parts in terms of solidcontent of polyvinylidene fluoride (produced by Kureha Corporation;product name: #7208) as a binder, and N-methylpyrrolidone as a solventsuch that the total solid content concentration was 70%, and mixingthese materials using a planetary mixer.

The obtained slurry composition for a positive electrode mixed materiallayer was applied onto aluminum foil (current collector) of 20 μm inthickness by a comma coater such as to have a thickness after drying ofapproximately 150 μm. The applied slurry composition was dried byconveying the aluminum foil inside a 60° C. oven for 2 minutes at aspeed of 0.5 m/min. Thereafter, 2 minutes of heat treatment wasperformed at 120° C. to obtain a positive electrode web.

The positive electrode web was rolled by roll pressing to obtain apositive electrode having a positive electrode mixed material layerthickness of 55 μm.

<Preparation of Separator>

A separator made from a single layer of polypropylene (produced byCelgard, LLC.; product name: Celgard 2500) was used as a separator.

<Production of Lithium Ion Secondary Battery>

A rectangle of 49 cm×5 cm was cut out from the obtained positiveelectrode and was placed with the surface at the positive electrodemixed material layer side thereof facing upward. A separator that hadbeen cut out as 120 cm×5.5 cm was arranged on the positive electrodemixed material layer such that the positive electrode was positioned ata longitudinal direction left-hand side of the separator. In addition, arectangle of 50 cm×5.2 cm was cut out from the obtained negativeelectrode and was arranged on the separator such that the surface at thenegative electrode mixed material layer side thereof faced toward theseparator and such that the negative electrode was positioned at alongitudinal direction right-hand side of the separator. The resultantstack was wound by a winding machine to obtain a roll. The roll wasenclosed in an aluminum packing case serving as a battery case,electrolyte solution (solvent: ethylene carbonate/diethylcarbonate/vinylene carbonate=68.5/30/1.5 (volume ratio); electrolyte:LiPF₆ of 1 M in concentration) was injected such that no air remained,and an opening of the aluminum packing case was closed by heat sealingat 150° C. to produce a wound lithium ion secondary battery having acapacity of 800 mAh. Good operation of the lithium ion secondary batterywas confirmed.

Various measurements and evaluations were performed by the previouslydescribed methods with respect to the particulate polymers A and B, thebinder composition, the slurry composition, the electrode (negativeelectrode), the secondary battery, and so forth obtained as describedabove. The results are shown in Table 1.

Examples 2 to 4 and 9

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that amounts in productionof the binder composition for a non-aqueous secondary battery negativeelectrode mixed material layer were changed such that the ratio of theparticulate polymer A and the particulate polymer B was as shown inTable 1. The results are shown in Table 1.

Examples 5, 8, and 10 to 12

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that mixing ratios inproduction of a particulate polymer A were changed such that thechemical composition of the particulate polymer A was as shown inTable 1. The results are shown in Table 1. Note that that the “Graftingstep” was not performed in Example 10.

Examples 6 and 7

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that mixing ratios inproduction of a particulate polymer B were changed such that thechemical composition of the particulate polymer B was as shown inTable 1. The results are shown in Table 1.

Examples 13 to 16

Various components shown in Table 1 were used in production of aparticulate polymer B in mixing ratios such that the chemicalcomposition of the particulate polymer B was as shown in Table 1. Withthe exception of the above, various operations, measurements, andevaluations were performed in the same way as in Example 1. The resultsare shown in Table 1.

Example 17

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that 1,3-butadiene was usedas an aliphatic conjugated diene monomer in production of a particulatepolymer A. The results are shown in Table 1.

Example 18

In production of a particulate polymer A, a block copolymer solution wasproduced and then hydrogenation of the block copolymer was carried outusing a Ti-based hydrogenation catalyst to obtain a hydrogenated blockcopolymer. The percentage hydrogenation as measured by ¹H-NMR was 98%.The hydrogenated block copolymer that was obtained was then subjected tooperations of phase-inversion emulsification, vacuum evaporation,concentration, and filtration in the same way as in Example 1 to obtaina water dispersion of a particulate polymer A. With the exception of theabove, various operations, measurements, and evaluations were performedin the same way as in Example 1. The results are shown in Table 1.

Example 19

In production of a particulate polymer A, a block copolymer solution wasproduced using 1,3-butadiene as an aliphatic conjugated diene monomerand then hydrogenation of the block copolymer was carried out using aTi-based hydrogenation catalyst to obtain a hydrogenated blockcopolymer. The percentage hydrogenation as measured by ¹H-NMR was 98%.The hydrogenated block copolymer that was obtained was then subjected tooperations of phase-inversion emulsification, vacuum evaporation,concentration, and filtration in the same way as in Example 1 to obtaina water dispersion of a particulate polymer A. With the exception of theabove, various operations, measurements, and evaluations were performedin the same way as in Example 1. The results are shown in Table 1.

Comparative Example 1

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that a particulate polymer Bwas not compounded in the binder composition. The results are shown inTable 1.

Comparative Example 2

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that a particulate polymer Awas not compounded in the binder composition. The results are shown inTable 1.

Comparative Example 3

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that a styrene-isoprenerandom copolymer (SIR) produced as described below was used instead ofthe particulate polymer A (specific block copolymer). The results areshown in Table 1.

<Production of Styrene-Isoprene Random Copolymer (SIR)>

When starting operations for producing a particulate polymer A in thesame way as in Example 1, styrene and isoprene were added at once into apressure-resistant reactor, and a polymerization reaction was initiated.

Note that 233.3 kg of cyclohexane, 60.0 mmol ofN,N,N′,N′-tetramethylethylenediamine (hereinafter, referred to asTMEDA), 24.0 kg of styrene, and 76.0 kg of isoprene were added into thepressure-resistant reactor. These materials were stirred at 40° C. while2000.0 mmol of n-butyllithium was added thereto, and 1 hour ofpolymerization was performed while adjusting the temperature to 50° C.to 60° C. The polymerization conversion rate was 100%.

The resultant styrene-isoprene random copolymer (SIR) was subjected to agrafting step in the same way as in Example 1 to obtain a waterdispersion containing a styrene-isoprene random copolymer (SIR).

Comparative Examples 4 and 5

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that mixing ratios inproduction of a particulate polymer B were changed such that thechemical composition of the particulate polymer B was as shown inTable 1. The results are shown in Table 1.

In Table 1, shown below:

“SIS” indicates block copolymer having styrene region-isopreneregion-styrene region;

“SBS” indicates block copolymer having styrene region-butadieneregion-styrene region;

“SEPS” indicates block copolymer having styrene region-ethyleneregion/propylene region-styrene region;

“SEBS” indicates block copolymer having styrene region-ethyleneregion/butadiene region-styrene region;

“SIR” indicates random copolymer that is styrene isoprene rubber;

“ST” indicates styrene unit;

“IP” indicates isoprene unit;

“Hydrogenated IP” indicates hydrogenated isoprene unit;

“BD” indicates 1,3-butadiene unit;

“Hydrogenated BD” indicates hydrogenated butadiene unit;

“MAA” indicates methacrylic acid unit;

“2EHA” indicates 2-ethylhexyl acrylate unit;

“AA” indicates acrylic acid unit;

“βHEA” indicates 2-hydroxyethyl acrylate unit;

“HEMA” indicates 2-hydroxyethyl methacrylate unit;

“AGE” indicates allyl glycidyl ether unit;

“AMA” indicates allyl methacrylate unit; and

“DVB” indicates divinylbenzene unit.

TABLE 1 Examples 1 2 3 4 5 6 7 8 9 Binder Particulate Type SIS SIS SISSIS SIS SIS SIS SIS SIS compo- polymer Block structure Yes Yes Yes YesYes Yes Yes Yes Yes sition A Graft portion Yes Yes Yes Yes Yes Yes YesYes Yes for Aromatic vinyl Type ST ST ST ST ST ST ST ST ST non- monomerunit Proportion 23.0 23.0 23.0 23.0 11.0 23.0 23.0 23.0 23.0 aqueous(mass %) sec- ondary Aliphatic con- Type IP IP IP IP IP IP IP IP IPbattery jugated diene elec- monomer trode unit Proportion 74.0 74.0 74.074.0 86.0 74.0 74.0 76.8 74.0 (mass %) Acidic group- Type MAA MAA MAAMAA MAA MAA MAA MAA MAA containing Proportion 3.0 3.0 3.0 3.0 3.0 3.03.0 0.2 3.0 monomer unit (mass %) Diblock content (mass %) 15 15 15 1515 15 15 15 15 Volume-average particle 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.01.0 diameter (μm) Particulate (Meth)acrylic acid Type 2EHA 2EHA 2EHA2EHA 2EHA 2EHA 2EHA 2EHA 2EHA polymer ester monomer unit Proportion 64.164.1 64.1 64.1 64.1 80.0 25.0 64.1 64.1 B (mass %) Aromatic vinyl TypeSt St St St St St St St St monomer unit Proportion 30.0 30.0 30.0 30.030.0 14.1 69.1 30.0 30.0 (mass %) Vinyl cyanide Type — — — — — — — — —monomer unit Proportion — — — — — — — — — (mass %) Acidic group- Type AAAA AA AA AA AA AA AA AA containing mono- Proportion 4.0 4.0 4.0 4.0 4.04.0 4.0 4.0 4.0 mer unit (mass %) Polar group- Type — — — — — — — — —containing ethylenically Proportion — — — — — — — — — unsaturated car-(mass %) boxylic acid ester monomer unit Cross-linkable Type AGE/ AGE/AGE/ AGE/ AGE/ AGE/ AGE/ AGE/ AGE/ monomer unit AMA AMA AMA AMA AMA AMAAMA AMA AMA Proportion 1.7/ 1.7/ 1.7/ 1.7/ 1.7/ 1.7/ 1.7/ 1.7/ 1.7/(mass %) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Volume-average particle0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 diameter (μm) Content ratio(polymer A:polymer B) 50:50 65:35 35:65 25:75 50:50 50:50 50:50 50:5090:10 Electrode Negative electrode mixed material 1.75 1.75 1.75 1.751.75 1.75 1.75 1.75 1.75 layer density (g/cm³) Eval- Slurry stability AA A A B A A B A uation Electrode swelling A A A A C B A B BInjectability A A A A A A A B C Low-temperature output A A A A A A C B Ccharacteristics Cycle characteristics A A A B B C B B B Examples 10 1112 13 14 15 16 17 18 19 Binder SIS SIS SIS SIS SIS SIS SIS SBS SEPS SEBScompo- Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes sition No Yes Yes Yes YesYes Yes Yes No No for ST ST ST ST ST ST ST ST ST ST non- 22.0 3.0 75.023.0 23.0 23.0 23.0 23.0 23.0 23.0 aqueous sec- ondary IP IP IP IP IP IPIP BD Hydro- Hydro- battery gen- gen- elec- ated ated trode IP BD 78.094.0 22.0 74.0 74.0 74.0 74.0 74.0 77.0 77.0 — MAA MAA MAA MAA MAA MAAMAA — — — 3.0 3.0 3.0 3.0 3.0 3.0 3.0 — — 15 15 15 15 15 15 15 15 15 151.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 2EHA 2EHA 2EHA 2EHA 2EHA 2EHA BA2EHA 2EHA 2EHA 64.1 64.1 64.1 75.0 50.5 30.0 60.0 64.1 64.1 64.1 St StSt — St St St St St St 30.0 30.0 30.0 — 44.0 65.0 30.0 30.0 30.0 30.0 —— — AN — — — — — — — — — 22.0 — — — — — — AA AA AA IA AA IA AA AA AA AA4.0 4.0 4.0 2.0 3.0 2.5 9.5 4.0 4.0 4.0 — — — βHEA HEMA HEMA — — — — — —— 1 2 2 — — — — AGE/ AGE/ AGE/ — DVB DVB AMA AGE/ AGE/ AGE/ AMA AMA AMAAMA AMA AMA 1.7/ 1.7/ 1.7/ — 0.5 0.5 0.5 1.7/ 1.7/ 1.7/ 0.2 0.2 0.2 0.20.2 0.2 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 50:50 50:5050:50 50:50 50:50 50:50 50:50 50:50 50:50 50:50 Electrode 1.75 1.75 1.751.75 1.75 1.75 1.75 1.75 1.75 1.75 Eval- C B A B A A A A C C uation C CC C A A B B B B B A C A A A A A A A C B B B A A B A B B C C C C A B B BB B Comparative examples 1 2 3 4 5 Binder SIS — SIR SIS SIS compo- Yes —No Yes Yes sition Yes — Yes Yes Yes for ST — ST ST ST non- 23.0 — 23.023.0 23.0 aqueous sec- ondary IP — IP IP IP battery elec- trode 74.0 —74.0 74.0 74.0 MAA — MAA MAA MAA 3.0 — 3.0 3.0 3.0 15 — — 15 15 1.0 —1.0 1.0 1.0 — 2EHA 2EHA 2EHA 2EHA — 64.1 64.1 10.0 90.0 — St St St St —30.0 30.0 84.1 4.1 — — — — — — — — — — — AA AA AA AA — 4.0 4.0 4.0 4.0 —— — — — — — — — — — AGE/ AGE/ AGE/ AGE/ AMA AMA AMA AMA — 1.7/ 1.7/ 1.7/1.7/ 0.2 0.2 0.2 0.2 — 0.15 0.15 0.15 0.15 100:0 0:100 50:50 50:50 50:50Electrode 1.75 1.75 1.75 1.75 1.75 Eval- A A A A A uation C D D C D D AA B A D C C D C C D D C D

It can be seen from Table 1 that it was possible to improvelow-temperature output characteristics and cycle characteristics of anobtained secondary battery in Examples 1 to 19 in which the used bindercomposition contained both a particulate polymer A that was a blockcopolymer including an aromatic vinyl monomer unit and an aliphaticconjugated diene monomer unit having a carbon number of 4 or more and aparticulate polymer B that was a random copolymer including a(meth)acrylic acid ester monomer unit in a proportion of not less than20 mass % and not more than 80 mass %.

On the other hand, it can be seen that it was not possible to enhancelow-temperature output characteristics and cycle characteristics of anobtained secondary battery in Comparative Examples 1 and 2 in whicheither a particulate polymer A or a particulate polymer B such asdescribed above was absent, Comparative Example 3 in which styreneisoprene rubber (random copolymer) was used instead of a particulatepolymer A satisfying the specific conditions described above, andComparative Examples 4 and 5 in which the proportion in which aparticulate polymer B included a (meth)acrylic acid ester monomer unitwas outside of the specific range set forth above.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a bindercomposition for a non-aqueous secondary battery electrode and a slurrycomposition for a non-aqueous secondary battery electrode with which itis possible to form an electrode for a non-aqueous secondary batterythat can cause a non-aqueous secondary battery to display excellentlow-temperature output characteristics and cycle characteristics.

Moreover, according to the present disclosure, it is possible to providean electrode for a non-aqueous secondary battery that can cause anon-aqueous secondary battery to display excellent low-temperatureoutput characteristics and cycle characteristics.

Furthermore, according to the present disclosure, it is possible toprovide a non-aqueous secondary battery having excellent batterycharacteristics such as low-temperature output characteristics and cyclecharacteristics.

1. A binder composition for a non-aqueous secondary battery electrodecomprising a particulate polymer A and a particulate polymer B, whereinthe particulate polymer A is a block copolymer including an aromaticvinyl monomer unit and an aliphatic conjugated diene monomer unit havinga carbon number of 4 or more, and the particulate polymer B is a randomcopolymer including a (meth)acrylic acid ester monomer unit in aproportion of not less than 20.0 mass % and not more than 80.0 mass %.2. The binder composition for a non-aqueous secondary battery electrodeaccording to claim 1, wherein the particulate polymer A includes a graftportion.
 3. The binder composition for a non-aqueous secondary batteryelectrode according to claim 2, wherein the graft portion of theparticulate polymer A includes an acidic group-containing monomer unitin a proportion of not less than 0.1 mass % and not more than 30.0 mass% when the particulate polymer A is taken to be 100 mass % overall. 4.The binder composition for a non-aqueous secondary battery electrodeaccording to claim 1, wherein the particulate polymer A includes thearomatic vinyl monomer unit in a proportion of not less than 10.0 mass %and not more than 30.0 mass %.
 5. The binder composition for anon-aqueous secondary battery electrode according to claim 1, whereincontent of the particulate polymer A is not less than 20.0 mass % andnot more than 80.0 mass % when total content of the particulate polymerA and the particulate polymer B is taken to be 100 mass %.
 6. The bindercomposition for a non-aqueous secondary battery electrode according toclaim 1, wherein the particulate polymer B includes a monomer unitselected from an aromatic vinyl monomer unit and a vinyl cyanide monomerunit in a proportion of not less than 10 mass % and not more than 70mass %.
 7. The binder composition for a non-aqueous secondary batteryelectrode according to claim 1, wherein the particulate polymer Bfurther includes an acidic group-containing monomer unit in a proportionof not less than 1.0 mass % and not more than 15.0 mass %.
 8. A slurrycomposition for a non-aqueous secondary battery electrode comprising: anelectrode active material; and the binder composition for a non-aqueoussecondary battery electrode according to claim
 1. 9. An electrode for anon-aqueous secondary battery comprising an electrode mixed materiallayer formed using the slurry composition for a non-aqueous secondarybattery electrode according to claim 8, wherein the electrode mixedmaterial layer has a density of 1.70 g/cm³ or more.
 10. A non-aqueoussecondary battery comprising the electrode for a non-aqueous secondarybattery according to claim 9.